Method for improving gradation of light scattering photographic materials



United States Patent 3,149,971 METHOD FOR IMPRGVHNG GRADATION 0F MGR-ET SCATTERiNG PHQTQGRAPHEC MATERIALS Albert Baril, lira, Metairie, and Lloyd B. De Luca, New (Brie-ans, La, assignors to Kalvar Corporation, New Orleans, La., a corporation of Louisiana No Drawing. Filed Earn. 29, I963, Ser. No. 254,560 15 Claims. (Cl. 96-49) The present invention is concerned with improving the photographic characteristics of vesicular photographic materials in which opacity is achieved by means of light scattering centers as contrasted to photographic emulsions or the like in which opacity is achieved by means of light absorption. Broadly stated, such light scattering photographic materials or films comprise a supported or selfsupporting vehicle having a photolytic agent dispersed therein which, upon exposure and development, e.g., by applying heat, effects the formation of minute vesicles of gas in the areas exposed to light, the vesicles acting as light scattering centers. More particularly, the invention is concerned with improving the characteristics of the class of such materials in which the vehicle is a synthetic, water-insoluble, non-hygroscopic, non-water swelling highly linear thermoplastic polymer of a monomer containing a C C group.

Heretofore, these vesicular photographic materials have been of only limited use in certain applications because of the short gray scale, or high photographic gamma, they possessed. That is, in general, it is desirable to reduce the contrast or gamma of light scattering photographic materials. In the past, this has not been possible without sacrificing other desirable photometric characteristics. For example, in order to obtain a material with lower contrast, it has been necesary to reduce the maximum obtainable density which involves a loss in density range.

As a consequence of reducing the gamma, and since the maximum density and the amount of energy required to obtain the maximum density remain constant, an effective speed increase is obtained for all densities except the maximum density.

Another disadvantage of certain light scattering materials has been the occurrence of variations in photographic speed from one part or" the light sensitive film to another. This is believed to be due, in substatnial part, to the inhomogeneity of the solvent-solute ratio.

The principal object of the present invention is to eliminate the above-mentioned disadvantages, to effect an increase in photographic speed, and thereby broaden the utility of the vesicular photographic materials into those areas where low photographic gamma and increased uniform photographic speed are desired. Other objects will be hereinafter apparent.

Broadly stated, the objects of the invention are realized by means of a method which comprises treating the above type of vesicular photographic material or film, prior to exposure and development thereof, with a heated aqueous fluid. The eliect of the treatment on low speed, high scattering vesicular photographic material is to increase the threshold photographic sensitivity approximately ten told so that the exposure range is increased and the gamma consequently lowered, while the maximum obtainable density remains substantially the same. The results of the invention are surprising and unexpected but a possible explanation thereof may be that nucleating centers are formed which allow the photolytic driving force to more effectively form the light scattering centers, particularly in those areas in which the exposure, and, consequently, the photolytic driving force, are small. In other words, this treatment apparently amounts to a homogeneous readjustment of the solvent-solute ratio in the finished photographic material whereby the molecular structure of the vehicle is rearranged in such a way that the energy of the photolytic reaction is more efiiciently utilized during the development phase.

The aqeuous treating fluid of the invention may be liquid or steam. Among liquids, although water is acceptable, it is preferred to use aqueous saline (NaCl) solutions or aqueous solutions modified by any of various inorganic salts and/ or wetting agents, the wetting agents being used to obtain a uniform unstreaked dry surface after completion of the treatment. The concentration of salt in aqueous saline solution is desirably 0.5 N although a maximum concentration up to 1.0 N may be used.

The photographic materials to which the invention is applicable may be described as vesicular photographic elements capable of furnishing a record solely in the form of a distribution pattern of radiation scattering discontinuities formed within a vehicle which is optically substantially homogeneous, the element comprising a dry, water resistant, non-hygroscopic film having a permeability constant for nitrogen within the range of 8.6 10" and 8x 10- said constant being the number of cubic centimeters of nitrogen transmitted at 30 C. by an area of one square centimeter in one second when the pressure gradient is one centimeter of mercury per one centimeter of transmission thickness, the continuous phase of said film comprising a synthetic, water-insoluble, nonhygroscopic, non-water swelling, highly linear thermoplastic polymer of a monomer containing a C=C group, said film having substantially uniformly dispersed therein as the sole essential nonreactive image producing agent a light decomposable agent which is substantially non-reactive to said film, which, upon exposure to light, decomposes into products which are chemically substantially non-reactive to said film, said non-reactive products being volatile on warming said film to form said radiation scattering discontinuities only in the light-struck areas of said film. These include the light scattering material described in copending U.S. applications of James et al., Serial No. 623,050, filed November 19, 1956, now U.S. Patent 3,032,414, and of Glavin, Serial No. 467,359, filed November 8, 1954, now U.S. Patent 2,950,194, and the acrylate-acrylonitrile copolymers and methacryloni-trile homopolymers described in the applications of Parker and Mokler, Serial No. 173,342, filed February 15, 1962, and Serial No. 192,067, filed March 3, 1962, which, while highly useful without the present treatment, may be significantly improved by the process described herein. The most useful materials are the copolymers of vinylidene chloride with acrylonitrile, copolymers of ethyl acrylate with acrylonitrile and homopolymers of methacrylonitrile. In copolymers containing acrylonitrile, it appears from the evidence described in the following examples that increases in the proportion of acrylonitrile result in increased sensitivity to the treatment.

The vehicle may be supported as a coating on any suitable base, transparent or opaque, 'such as black paper, polyethylene terephthalate (Mylar), cellulose acetate, ethyl cellulose, etc.

The time and temperature of the treatment varies but the appropriate conditions can be determined readily by treating a set of films in various degrees and then exposing and developing them and determining photographic gamma in the conventional manner. Depending on the characteristics desired of the film, the appropriate treatment conditions can then be selected. Another test which can be used is the degree of fogging. The treatment causes a very mild milk-like opacity to form in the vehicles which is believed to be caused by minute cracks in the resins. Excessive treatment is indicated by any more than barely perceptible opacity or fogging.

In the case of liquid treating baths, the treatment ususateen ally will be in the range l2l2 F. for 10 to 300 seconds and these conditions are particularly satisfactory for vinylidene chloride-acrylonitrile copolymers. Treatments of these materials at lower temperatures require inconveniently long times. However, the ethyl acrylateacrylonitrile resins, which contain -85 mole percent acrylonitrile, are more sensitive to the treatment and temperatures as low or about F. may be used.

As mentioned above, steam or water vapor may also be used. Moist steam may cause droplets of water to condense on the film which act, it is believed, in the same manner as a liquid water bath, but dry steam may also be used. The best treatment at present is believed to be with dry saturated steam at about one atmosphere of pressure (212 F). Water vapor generally treats the films more slowly than liquid treating baths, so that its use is principally with the more sensitive vehicles. The temperatures will generally be higher up to those at which the photographic sensitizer or the resin will be damaged significantly. However, higher temperatures 7 generally require shorter treatment times.

It will be appreciated from the foregoing that the invention broadens out the field of use for light scattering photographic systems in general, and enables these systems, in applications where the amount of available light is controllable, to compare favorably with such light absorbing systems as the silver halide system.

The following examples are intended to further illustrate the invention, it being understood that the invention is not limited to the specific embodiments which are shown:

Example I A light scattering photographic element was prepared according to Example I of copending US. patent application Serial No. 623,050, now US. Patent 3,032,414, the element comprising a dispersion of p-diazodimethylaniline Zinc chloride in a Saran vehicle coated on a transparent ethyl cellulose film base. After the dispersion was coated and dried on the film base, it was irnmersed in water at a temperature of 190 E, for 20 seconds. The gamma of the resulting film was reduced from approximately 0.65 to approximately 0.26 and the exposure range increased by a factor of approximately 2.2. Substantially equivalent results were obtained using a black paper base for the film.

Example 11 A light scattering photographic element was prepared in the manner described in Example I of copending applicaion Serial No. 623,050, now US. Patent 3,032,414, using a black paper base material. After coating and curing, the resulting photographic material was immersed in an aqueous saline solution, one-half normal at a temperature of 190 F, for approximately 20 seconds. This treatment resulted in a reduction of the gamma from about 4 to about 0.70 and an increase of the exposure range by a factor of about 6.

Example 111 'Example I above was repeated on a light scattering photographic element comprising a Saran vehicle coated to about 0.7 mils thickness on a sheet of polyethylene terephthalate (Mylar), as described in Example ll of Serial No. 467,359, now U.S. Patent 2,950,194. After the element was finished by drying, it was immersed in a water bath at 190 F., for about seconds. The gamma was reduced from about 0.50 to 0.18 and the exposure factor was increased by a factor of about 3.5.

Example IV Example III was repeated except that the water bath was replaced by an aqueous saline solution (0.5 N) at F, for 10 seconds with the following results: Uniformity in photographic speed was obtained without any f d significant change in the photometric characteristics of the major portion of the emulsion.

Example V A light scattering photographic element was prepared according to Example l of copending U.S. patent application Serial No. 623,050, new US. Patent 3,032,414, the element comprising a dispersion of p-diazodimethylaniline zinc chloride in a Saran vehicle coated on a transparent ethyl cellulose film base. After the dispersion was coated and dried on the film base, it was immersed in gallons of water containing 284 grams hydroxyethyl-Z-heptadecenyl glyoxalidine and 190 cc. glacial acetic acid at a temperature of 190 F., for 20 seconds. The gamma of the resulting film was reduced from approximately 0.65 to approximately 0.26 and the exposure range increased by a factor of approximately 2.2.

Example VI A light scattering photographic element was prepared as in Example I using, as the Saran vehicle, a copolymer of vinylidene chloride and acrylonitrile containing 40 mole percent acrylonitrile, made by emulsion polymerization. The film was treated for 30 seconds in hot water at 200 F. and exposed for 20 seconds through a standard Eastman Kodak step Wedge. 5 to 6 additional steps of gradually decreasing photographic density are noted. When the same film is treated with dry saturated steam at atmospheric pressure at 212 F. for 12 minutes, only a very weak treatment takes place.

Example VII A film is prepared as in Example I using, as the Saran vehicle, a copolymer of vinylidene chloride and acrylonitrile containing 53 mole percent aciylonitrile. The film was given 30 second treatments in liquid water at 200 F. and 170 F. The treatment at 200 F. results in heavy over-all fogging of the unexposed film, but a satisfactory treatment is observed at 70 F. The film was also subjected to a treatment with steam at atmospheric pressure and 212 F., and a pronounced effect was observed on the photographic gamma.

Example VIII A photographic film was prepared as in Example ll of copending application Serial No. 173,342, filed February 15, 1962. When this was immersed in liquid water at F. for as short a time as 1 second, there was general fogging. However, a satisfactory treatment was observed at 120 F. for 45 seconds. A 60 second treatment at 120 F. was found to be excessive, and a 30 second trea ment at 120 F. gave a usable but lesser gain in sensitivity than observed at 45 seconds.

The same film was exposed to dry steam atmospheric pressure and 212 F. for 10 seconds. Exposure and development as in Example VI, using a standard Eastman Kodak step wedge, showed a gain of at least 5 additional steps of decreasing photographic density. The same film was also exposed to an air atmosphere at 100% relative humidity at 70 F. for 24 hours and a slight improvement-. 5

What is claimed is:

1. A method of improving the photographic sensitivity characteristics.

of a vesicular photographic element capable of furnishing a record solely in the form of a distribution pattern of a radiation scattering discontinuities formed Within a vehicle which is optically substantially homogeneous,

said element comprising a dry, water-resistant, nonhygroscopic film having a permeability constant for nitrogen Within the range of 8.6 X and 8 X l0 said constant being the number of cubic centimeters of nitrogen transmitted at 30 C. by an area of one square centimeter in one second when the pressure gradient is one centimeter of mercury per one centimeter of transmission thickness, the continuous phase of said film comprising a synthetic, Water-insoluble, non-hygroscopic, non-water swelling, highly linear thermoplastic polymer of a monomer containing a C=C group,

said film having substantially uniformly dispersed therein as the sole essential image-producing agent a light-decomposable agent While is substantially nonreactive to said film, which, upon exposure to light, decomposes into products which are chemically substantially non-reactive to said film, said non-reactive products being volatile on Warming said film to form said radiation scattering discontinuities only in the light-struck areas of said film,

said method of improving the photographic sensitivity characteristics comprising contacting said film with an aqueous fluid maintained at an elevated tempera ture before exposure to light and development.

2. A method of improving photographic sensitivity characteristics as set forth in claim 1 in which the temperature of the treatment is above about 100 F.

3. A method of improving photographic sensitivity characteristics as set forth in claim 1 in which the aqueous fluid is an aqueous liquid treating bath.

4. A method of improving photographic sensitivity characteristics as set forth in claim 3 in which said liquid bath is an aqueous salt bath.

5. A method of improving photographic sensitivity characteristics as set forth in claim 4 in which the liquid treating bath comprises a 0.5 normal aqueous solution of sodium chloride.

6. A method of improving photographic sensitivity characteristics as set forth in claim 3 in which the liquid treating bath contains hydroxyl ethyl heptadecenyl glyoxaldine and glacial acetic acid.

7. A method of improving photographic sensitivity characteristics as set forth in claim 3 in which the liquid treating bath contains a wetting agent.

8. A method of improving photographic sensitivity characteristics as set forth in claim 3 in which the photographic element is immersed in the liquid bath.

9. A method of improving photographic sensitivity characteristics as set forth in claim 1 in which said film contains a substantially non-volatile organic material which is compatible with said polymer so that said film is optically substantially homogeneous.

10. A method of improving photographic sensitivity characteristics as set forth in claim 1 in which said thermoplastic polymer contains polymerized acrylonitrile.

11. A method of improving photographic sensitivity characteristics as set forth in claim 1 in which said thermopiastic polymer comprises polyvinylidene chloride.

12. A method of improving photographic sensitivity characteristics as set forth in claim 1 in which said polymer comprises a copolymer of vinylidene chloride and acrylonitrile.

13. A method of improving photographic sensitivity characteristics as set forth in claim 12 in which said aqueous fluid is an aqueous liquid treating bath maintained at a temperature of l-2l2 F. and the treatment is for 10-300 seconds.

14. A method of improving photographic sensitivity characteristics as set forth in claim 1 in which the lightdecomposable agent is a diazo compound.

15. A method of manufacturing photographic sensitivity characteristics as set forth in claim 14 in which the diazo compound is p-diazodimethylaniline zinc chloride.

No references cited. 

1. A METHOD OF IMPROVING THE PHOTOGRAPHIC SENSITIVITY CHARACTERISTICS. OF A VESICULAR PHOTOGRAPHIC ELEMENT CAPABLE OF FURNISHING A RECORD SOLELY IN THE FORM OF A DISTRIBUTION PATTERN OF A RADIATION SCATTERING DISCONTINUITIES FORMED WITHIN A VEHICLE WHICH IS OPTICALLY SUBSTANTIALLY HOMOGENEOUS, SAID ELEMENT COMPRISING A DRY, WATER-RESISTANT, NONHYGROSCOPIC FILM HAVING A PERMEABILITY CONSTANT FOR NITROGEN WITHIN THE RANGE OF 8.6X10**-16 AND 8X10**-10, SAID CONSTANT BEING THE NUMBER OF CUBIC CENTIMETERS OF NITROGEN TRANSMITTED AT 30*C. BY AN AREA OF ONE SQUARE CENTIMETER IN ONE SECOND WHEN THE PRESSURE GRADIENT IS ONE CENTIMETER OF MERCURY PER ONE CENTIMETER OF TRANSMISSION THICKNESS, THE CONTINUOUS PHASE OF SAID FILM COMPRISING A SYNTHETIC, WATER-INSOLUBLE, NON-HYGROSCOPIC, NON-WATER SWELLING, HIGHLY LINEAR THERMOPLASTIC POYMER OF A MONOMER CONTAINING A >C=C< GROUP, SAID FILM HAVING SUBSTANTIALLY UNIFORMLY DISPERSED THEREIN AS THE SOLE ESSENTIAL IMAGE-PRODUCING AGENT A LIGHT-DECOMPOSABLE AGENT WHILE IS SUBSTANTIALLY NONREACTIVE TO SAID FILM, WHICH, UPON EXPOSURE TO LIGHT, DECOMPOSES INTO PRODUCTS WHICH ARE CHEMICALLY SUBSTANTIALLY NON-REACTIE TO SAID FILM, SAID NON-REACTIVE PRODUCTS BEING VOLATILE ON WARMING SAID FILM TO FORM SAID RADIATION SCATTERING DISCONTINUITIES ONLY IN THE LIGHT-STRUCK AREAS OF SAID FILM, SAID METHOD OF IMPROVING THE PHOTOGRAPHIC SENSITIVITY CHARACTERISTICS COMPRISING CONTACTING SAID FILM WITH AN AQUEOUS FLUID MAINTGAINED AT AN ELEVATED TEMPERATURE BEFORE EXPOSURE TO LIGHT AND DEVELOPMENT. 